R. Vdovjak, P. Barna, and G. Houben. Advanced Information System Engineering, 15th
International Conference, CAiSE 2003, volume 2681 of Lecture Notes in Computer Science, Klagenfurt/Velden, Austria, Springer-Verlag, (June 2003)
A. Levy, A. Rajaraman, and J. Ordille. Proceedings of the 22nd International Conference on Very
Large Databases, VLDB-96, page 251--262. Bombay, India, (1996)